Regions of MEMS (micro electro mechanical systems) technology attracting attention today include bio analyses, environment analyses and chemical syntheses. Micro-fluid devices or so-called μTAS (micro total analysis systems) are known as devices useful for such analyses and syntheses.
A micro-fluid device is formed by providing a substrate, which is typically made of a semiconductor, glass, ceramic or plastic, with a fluid channel therein and a liquid substance that may be a specimen to be analyzed or a material to be used for a chemical synthesis is made to flow there for the analysis or the synthesis, whichever appropriate.
There is a demand for devices that can reduce the consumption of solvents, specimens and reagents and realize a faster reaction speed to exploit the advantages of microscale if compared with conventional analysis methods or batch treatments and for apparatus systems using such devices.
Known liquid conveying methods for micro-fluid devices include those using piezoelectric devices (Takaaki Suzuki et al., The 10th International Conference on Miniaturized Systems for Chemistry and Life Sciences (μTAS2006) vol. 1, pp. 131-133).
FIG. 5 is a schematic cross sectional view of a known arrangement for conveying liquid. In FIG. 5, reference symbol 100 denotes a micro-fluid device. A fluid channel 110 is formed in the inside of the micro-fluid device 100, while a fixed wall 120 and a movable wall 130 are formed as fluid channel walls. The movable wall 130 is provided with a plurality of projections 135 and piezoelectric devices 140 are arranged at the projections 135. The piezoelectric devices 140 oscillate vertically as illustrated in FIG. 5 when the phases of the voltages being applied to the respective piezoelectric devices 140 are shifted temporarily. Then, as a result, a traveling wave is produced on the movable wall 130. The liquid in the fluid channel 110 can be conveyed, while being agitated, by utilizing the traveling wave.
To be more specific, as the movement of the liquid that is found in the fluid channel 110 and driven to move in the x- and y-directions (or three-dimensionally also in the z-direction) as illustrated in FIG. 5 is averaged, the liquid in the fluid channel 110 is driven to move in the direction of the traveling wave as a result. Therefore, the liquid can be conveyed in a desired liquid conveying direction by controlling the voltages being applied to the respective piezoelectric devices 140 so as to produce a traveling wave in the desired liquid conveying direction.
However, the above described known technique is accompanied by the following problems.
With the liquid conveying method using a traveling wave, the liquid is driven to move back and forth along the liquid conveying direction until it is driven to move in the direction of the traveling wave as a result. Thus, the liquid conveying efficiency of this liquid conveying method is not necessarily high. To improve the liquid conveying efficiency, the liquid is preferably driven to move back and forth to a lesser extent. For this purpose, the piezoelectric devices 140 should be oscillated so as to make the traveling wave proceed with a lower frequency and a greater amplitude. However, it is difficult to do so because the displacement that each piezoelectric device 140 can illustrate is very small.
Additionally, a large number of piezoelectric devices 140 are required to produce a traveling wave. Then, so many signal generators and amplifiers need to be brought in. As a result, the arrangement for handling the micro-fluid device 100 can become large and costly. Furthermore, since the piezoelectric devices 140 are arranged directly in the micro-fluid device 100, the micro-fluid device 100 should carry a high price tag per se.
Finally, the micro-fluid device 100 illustrates large dimensions that reflect the number of the piezoelectric devices 140 arranged therein.